Veterinary Surgery
39:2–13, 2010
INVITED REVIEW
Feline Degenerative Joint Disease
B. DUNCAN X. LASCELLES,
BSc, BVSc, PhD, DSAS(ST), Diplomate ACVS & ECVS
Objective: To critically review and collate published information on feline degenerative joint disease
(DJD) and identify areas in which information is lacking.
Study Design: Critical literature review.
Methods: Literature search through Pub Med, Commonwealth Agricultural Bureau Abstracts
published in the English Language, or translated into English (January 1940–August 2008).
Results: Although there are no prospective studies, the prevalence of radiographic DJD appears to
be high and can be associated with clinical signs of decreased mobility. There appears to be a
mismatch between radiographic and clinical examination ﬁndings (pain response). There is little
information on the cause of DJD in different joints. There are no fully validated subjective or
objective assessment systems for the measurement of chronic DJD-associated pain in the cat.
Development of a feline model of chronic DJD-associated pain may speed the development and
evaluation of candidate pain-alleviating compounds and treatments.
Conclusions: The high prevalence of feline DJD and lack of information about it, suggests further
investigation is needed.
Clinical Relevance: Feline DJD occurs with high frequency, and yet there is little to guide the
clinician on prevention or treatment.
r Copyright 2010 by The American College of Veterinary Surgeons
the evidence for efﬁcacy of postulated treatments for
this pain.
All mammals develop DJD, the progressive destruction of one or more components of joints—cartilage,
subchondral bone, ligaments, and joint capsule. DJD
affects synovial and cartilaginous joints but not ﬁbrous
joints (synarthroses). In synovial joints, degeneration is
typically associated with variable synovial thickening, articular cartilage degeneration, subchondral bone sclerosis, periarticular osteophyte formation, and joint capsule
thickening.3 For cartilaginous joints of the spinal column,
degeneration generally results from degeneration of the
intervertebral disk, with narrowing of the intervertebral
space, sclerosis of the endplate, and formation of
osteophytes (spondylosis deformans).4
INTRODUCTION
S
URPRISINGLY LITTLE is known about feline
degenerative joint disease (DJD) although there
have been recent attempts to characterize feline joint disease based on radiographic changes and to evaluate associated clinical signs.1,2 Concurrently, there has been
much speculation on feline DJD and likely, many erroneous presumptions based on DJD in other species
especially in non-peer-reviewed literature. Thus, it seems
timely to critically review what is known about feline
DJD and to identify needed information to appropriately
address this clinical entity. This review concentrates on
the prevalence and causes of feline DJD, evaluates
whether feline DJD is associated with pain, and reviews
From the Comparative Pain Research Laboratory and Surgery Section, Department of Clinical Sciences, College of Veterinary
Medicine, North Carolina State University, Raleigh, NC.
Corresponding author: B. Duncan X. Lascelles, BSc, BVSc, PhD, DSAS(ST), Diplomate ACVS & ECVS Surgery Section, Department of Clinical Sciences, North Carolina State University, 4700 Hillsborough Street, Raleigh, NC 27606. E-mail: [email protected].
Submitted June 2008; Accepted February 2009
r Copyright 2010 by The American College of Veterinary Surgeons
0161-3499/09
doi:10.1111/j.1532-950X.2009.00597.x
2
LASCELLES
Primary DJD is an idiopathic phenomenon occurring
without an apparent initiating factor whereas secondary
DJD results from some predisposing condition, usually
trauma. Primary osteoarthritis (OA), the most common
form of primary DJD, is likely related to aging and typically occurs in older individuals. For feline synovial
joints, there are several recognized and postulated primary and secondary causes of joint degeneration. DJD
associated with Scottish Fold osteochondrodysplasia,5
mucopolysaccharidosis (MPS),6 and age-related cartilage
degeneration has been described as primary DJD.7 Postulated secondary causes of DJD in cats are congenital,
trauma, infectious and inﬂammatory, nutritional, and
immune-mediated,7 although there is little evidence for
many of these causes.
Radiographic Prevalence of Feline DJD
Axial Skeleton. In the ﬁrst extensive radiographic
evaluation of DJD of the feline axial skeleton,8 a single
lateral radiograph of the entire vertebral column was
taken of 150 cadavers of older cats before soft tissues
were removed and the vertebral column inspected for
osteophytes. Although osteophytes were observed in 68%
of cats, only 85% were evident on lateral radiographs.
New bone formation was termed ‘‘vertebral osteophytes’’
because little was known about the cause of the condition. Cervical vertebrae were seemingly equally affected
with a sharp increase in prevalence of degenerative
changes at the cervicothoracic junction. All thoracic vertebrae appeared commonly affected, with a peak incidence between the 7th and 8th vertebrae. Lumbar
vertebrae were affected more than cervical, but less than
thoracic, vertebrae. In the thoracic region, the cranial
aspects of the vertebrae were more often affected whereas
in the lumbar region, the caudal aspects of vertebrae were
more often affected.8
Hardie et al9 retrospectively reviewed radiographs of
100 cats 412 years old that had spinal radiography at a
north American veterinary teaching hospital as part of a
diagnostic workup for various conditions. Radiographs
were included if any of the axial or appendicular skeletal
joints were imaged. The vertebral column was divided into
thoracic, lumbar, and lumbosacral regions, with the sternal articulations grouped together. Each visible articulation was scored for DJD according to Morgan.10 Lateral
and ventral enthesiophytes, narrowing of intervertebral
spaces, and apparent vertebral endplate sclerosis were recorded. Consistently viewed axial segments were the thoracic vertebral column (96 cats), sternum (92 cats), lumbar
(30 cats), and lumbosacral vertebral column (18 cats).
DJD was identiﬁed in 80 cats and in 26, only the vertebral
column was involved with the most severely affected area
being, the lumbosacral junction.
3
In a similar study at a Scottish veterinary teaching hospital,11 radiographs of 218 cats (mean age, 6.5 years) were
examined. Recorded axial skeleton (classiﬁed as cervical,
thoracic, lumbar, lumbosacral, and sternal segments) abnormalities were enthesiophytes at 1 intervertebral
joints, mineralization of any intervertebral disk, collapse
of joint spaces, or osteophytosis of any of the articular
facets. The authors considered ‘‘enthesiophytes’’ a more
appropriate term than ‘‘vertebral osteophytes’’8 because
degeneration involved an enthesis.12 Of 1090 axial segments that could potentially have been radiographed in
218 cats, 513 axial segments had radiographs made of
them. Axial skeletal DJD was evident in 45 (21%) cats,
with only the sternal segment affected in 11 cats, spondylosis deformans in 17 cats, spondylosis deformans and sternal DJD in 16, and mineralized intervertebral disks in 1
cat. Spondylosis deformans was most commonly seen in
the thoracic segment, at T7–8 and T9–10, ﬁndings very
similar to Beadman et al.8 The most severe DJD was observed in the lumbar segment, in contrast to Hardie et al9
where the most severe lesions involved the lumbosacral
joint.
Thoracic articular facet OA was reported in 6 (the
subgroup that had obvious joint pain) of 25 cats that had
complete skeletal radiography in a study evaluating clinical signs associated with appendicular joint OA.1 In another study evaluating measures of pain relief in cats with
appendicular joint OA, 12 of 13 cats (mean age, 14 years)
had radiographic changes in the spinal column consisting
of spondylosis deformans and/or radiographic signs consistent with intervertebral disk disease.11
Skeletal joint pathology has been evaluated in nondomesticated felidae.13 Visual examinations of 386 big
cat skeletons (e.g., leopard, mountain lion, African lion)
in various north American collections revealed
spondyloarthropathy in 3.6% of skeletons. Spondyloarthropathy was deﬁned as evidence of facet joint or sacroiliac joint erosion or fusion, asymmetrical pattern of
arthritis, reactive new bone formation, syndesmophytes
(calciﬁcation within the annulus ﬁbrosus), or peripheral
joint fusion. In reviewing the report, seemingly axial degenerative changes were evident in 2.1%.
Although it appears that investigators are describing
the same general ﬁndings for axial skeleton DJD, the
nomenclature used varies. Most refer to spondylosis
deformans2,11 (earlier referred to as vertebral osteophytosis8) to describe new bone observed on ventral and lateral
aspects of axial skeleton vertebrae; however, spondyloarthropathy has also been used.9,11,13 In humans, spondyloarthropathies are generally considered a group of
related inﬂammatory joint diseases often associated with
the MHC class I molecule HLA-B2714: ankylosing
spondylitis, reactive arthritis, arthritis associated with inﬂammatory bowel disease, and psoriatic arthritis. In hu-
4
FELINE DEGENERATIVE JOINT DISEASE
Table 1. Summary Findings of the Reported Prevalence of Radiographic Signs of Axial Skeleton Degenerative Joint Disease in Domesticated Cats
Mean Cat
Age (Years)
Unknown (older)
15
6.5
11
14
% of Cats with
Axial Skeleton DJD
Most Commonly
Affected Area
Most Severely
Affected Area
Reference
58
80
21
–
92
Thoracic (T7–8)
—
Thoracic (T6–7, 9–10)
Thoracic
Thoracic
—
Lumbosacral
Lumbar
Thoracic
–
Beadman et al8
Hardie et al9
Clarke et al11
Clarke & Bennett1
Lascelles et al84
For some entries, data cannot be given because of the design or nature of the study (see text for full details). The deﬁnition of osteoarthritis and
degenerative joint disease (DJD) varies between studies.
mans, the axial skeleton (particularly the sacroiliac joint) is
often affected by these spondyloarthropathies; however, in
its most accurate deﬁnition, it includes appendicular joint
pathology as occurs in Reiter’s syndrome.14 Until more is
known about the histopathologic characteristics and
cause(s) of the axial skeleton changes observed in felidae,
spondylosis deformans, and facet joint DJD are the most
appropriate descriptive terms. Given the possibility that
true spondyloarthropathies might occur in felidae, it will
be important for future studies to evaluate both appendicular and axial skeletal changes in detail, evaluating the
microscopic changes associated with radiographic
changes, and any association with concurrent diseases.
Summarily, published reports suggest that the most
frequent site of axial skeleton DJD in cats is T7–10 with
the most severe lesions occurring in the lumbar or
lumbosacral region (Table 1). Clearly, the incidence of
axial skeleton DJD is markedly different between studies.
This may reﬂect differences in how DJD was classiﬁed,
but more likely reﬂects age differences in study populations with Beadman et al8 observing axial skeleton DJD
increasing in frequency with age.
Appendicular Skeleton. Langenbach et al15 prospectively evaluated the relationship between DJD and hip
joint laxity in a nonrandomly selected group of 78 cats
(mean age, 2.5 years; range, 6 months–9 years old); 22%
were domestic shorthairs and 78% were purebreds from 8
different breeds. Orthogonal views were evaluated for
DJD using radiographic criteria established for DJD in
dogs.16 Hip dysplasia (HD) was found in 25 (32%) cats
and DJD in 19%, with all cats with DJD having HD.
Keller et al17 retrospectively evaluated cats, admitted to a
north American veterinary teaching hospital, with ventrodorsal radiographic projections of the coxofemoral
joints. Of 684 cats (mean age, 2.8 years), 6.6% (45 cats)
had HD and 43 of these had concurrent coxofemoral
joint DJD. Interestingly, the DJD was described as being
different in appearance compared with DJD in dogs, with
extensive remodeling and proliferative changes involving
the craniodorsal acetabular margin and minimal remodeling of the femoral neck (Fig 1).17
Hardie et al9 evaluated appendicular skeleton radiographs, scored according to Morgan,10 in 100 cats (mean
age, 15 years; 68 domestic shorthairs, 17 domestic long
hairs, 15 other) considering the primary joints of the limb
individually and the joints of the feet as a single location.
The most consistently examined joints were the elbow (71
cats), coxofemoral (18), and stiﬂe (13) joints with the
carpus, tarsus, and feet each examined in only 2 cats.
DJD was observed in at least 1 appendicular joint in 64%
of cats with the elbow, most severely affected. In non-
Fig 1. Ventrodorsal projection of the coxofemoral joints.
There a proliferative changes involving the craniodorsal acetabular margin and minimal remodeling of the femoral neck.
LASCELLES
domesticated felidae,13 DJD was identiﬁed in 5.2% of the
big cats with the elbow being most commonly affected,
followed by the stiﬂe and shoulder.
In a study evaluating feline shoulder and stiﬂe synovial
ﬂuid, radiographs of all thoracic and pelvic limb joints
(except the hip) were obtained.18 Of 52 cats evaluated,
estimated age was distributed as o1-year-old (48%), 1–3
years (27%), 3–6 years (21%), and 46 years (4%). Sixteen cats (30%) had radiographic evidence of OA involving at least 1 joint, with the elbow being most
frequently affected (21% of elbow joints examined) and
although examined by a single radiologist, the criteria for
diagnosing OA were not deﬁned.
Clarke et al11 deﬁned appendicular DJD as presence of
periarticular and/or juxta-articular enthesiophytes, periarticular and intraarticular soft tissue mineralization,
or OA where OA was deﬁned as the radiographic presence of osteophytes, either with or without subchondral
sclerosis, soft tissue mineralization, and enthesiophytes.
Overall, 26% (605) of the total number (2616) of main
appendicular joints (shoulder, elbow, carpus, hip, stiﬂe,
and hock) were available for radiographic evaluation.
Of 218 cats (mean age, 6.5 years), 50 (23%; mean age,
10 years) had DJD of at least 1 appendicular joint
(36 had OA, 6 enthesiopathy [affecting 13 different
joints], and 8 had soft tissue mineralization [affecting elbows]). Normalized for the number of joints of each type
examined, the most commonly affected joints were the
hip (22%), elbow (16.4%), and stiﬂe (8.2%); however,
o7% of carpi and tarsi were visible on radiographs. In
a similar study of 292 sets of feline radiographs (mean cat
age not reported but mean age of clinic population, 8.2
years) evaluated for appendicular OA (deﬁned as increased subchondral bone density or periarticular new
bone),19 63 (22%) had OA of at least 1 appendicular joint
(mean age, 10.2 years). No obvious cause of OA was
identiﬁed in 56 cats and lesions were bilaterally symmetrical in 41 (73%), with the elbow most commonly
affected.
Clarke and Bennett,1 reported details of affected joints
in 25 of 28 cats. These cats were those with obvious pain
associated with manipulation of at least 1 joint with radiographic OA. In this group, the elbow, hip, and then
hock were the most commonly affected joints. In another
study evaluating measurement of chronic musculoskeletal
pain in cats,2 13 cats (mean age, 14 years) had every joint
evaluated radiographically and a median of 4 appendicular joints in each cat had radiographic signs consistent
with OA with the hip (16 joints) being most commonly
affected, followed by elbow (11), and tarsus (11), then
stiﬂe (10), shoulder (5), and carpus (2).
Ossicles can be found consistently in the menisci of
various mammalian species—rats, mice, hamsters—usually, in the cranial horn of the medial or lateral menisci
5
and have been described as not being a cause of, or associated with, DJD.20 However in 3 cats with meniscal
ossicles, it was suggested that the observed mineralization
was a primary, naturally occurring vestigial structure in 1
cat, and, trauma associated in another,21 and both cats
had DJD. When identiﬁed radiographically in 23 of 28
skeletally mature large nondomestic cats, they were considered a normal structure.22 Thus, it is unclear if meniscal ossicles in domestic cats (Figs 2 and 3) are indicative
of DJD, and radiologic and histologic studies are
required.
Summarily, the appendicular joints most commonly
affected by DJD are the hip and elbow, followed by the
stiﬂe or possibly tarsus (Table 2); however, there are no
reports where every joint in a randomly selected population of cats has been evaluated to ascertain the prevalence of DJD in cats. Further, similar to axial skeleton
lesions, DJD is deﬁned differently among studies. Hardie
et al9 claimed that all joints with radiographic signs of
DJD were osteoarthritic whereas Clarke et al11 attempted
to distinguish between radiographic signs of DJD, like
enthesiophytes and soft tissue mineralization (which, may
not represent OA [Fig 4]) and OA. Seemingly, there are
no studies in cats comparing the radiographic appearance
of joints with histologic ﬁndings. Such comparison is
needed to improve radiographic interpretation and to
address the suggestion that feline DJD may be associated
with less tendency for new bone formation compared
with some species.9,11
Fig 2. Lateral projection of the stiﬂe. Meniscal calciﬁcation
(conﬁrmed histologically) is evident with apparent associated
degenerative joint disease.
6
FELINE DEGENERATIVE JOINT DISEASE
Fig 3. Lateral projection of the stiﬂe. There is marked
meniscal calciﬁcation (conﬁrmed histologically) and associated
degenerative joint disease.
Causes of Feline DJD
Although Allan outlined common causes of OA in
cats,7 there is little documented supporting evidence and
most studies evaluating prevalence speculate on the cause
of DJD. Clarke et al11 indicated that 25% of OA cases
resulted from trauma, with 450% of cases having no
obvious cause suggesting that they may have been primary OA. Godfrey19 suggested only 13% of OA cases
were secondary to a disease generally recognized as lead-
ing to OA, thus 87% were possibly primary OA, predicated on an absence of underlying disease typically
considered to lead to secondary OA in other species.
However, as Godfrey indicates, this approach has not
been validated and it is unlikely that all cats were evaluated thoroughly enough during their lifetimes to rule
out possible causes of DJD. Hardie et al9 found little
evidence in medical records to indicate likely cause of
DJD and postulated that observed OA/DJD was likely
secondary to undetermined factors (e.g., elbow dysplasia,
chronic low-grade trauma, subtle malarticulation).
Of interest is the frequent bilateral occurrence of feline
DJD,1,2,19 a characteristic of DJD caused by bilateral
congenital malformations (e.g., joint dysplasia, osteochondrosis), systemic factors (e.g., endocrinopathy, metabolic disorders), neurogenic factors, chronic overuse, or
possible primary OA. In a case report of arthroscopic
debridement of bone fragments from an elbow joint with
DJD and associated lameness, it was suggested, but not
conﬁrmed, that the cause may have been fragmented
medial coronoid process.23 There are no reports of fragmented coronoid process in the cat.
The comparatively low incidence of appendicular joint
DJD and OA in big (e.g., leopard, mountain lion, African
lion) cats (5.2%) is interesting13; however, because age
was unknown the low incidence may reﬂect studying a
younger population. Regardless, other studies15,17,18 seem
to suggest that prevalence of DJD in young domestic cats
is substantially higher. Of 386 big cat specimens,13 283
were wild caught, and differences in lifestyle and diet between wild and domesticated cats may well account for
the apparent differences. Interestingly, disease that Rothschild et al13 classiﬁed as OA did not occur in wild
caught big cats.
Two primary forms of OA are fairly well recognized
in cats: Scottish Fold osteochondrodysplasia5,24,25 and
MPS.6,26–32 The Scottish Fold is a purebred cat with
generalized defective cartilage metabolism. The underly-
Table 2. Summary Findings of Studies Evaluating Prevalence of Radiographic Signs of Osteoarthritis (OA) or Degenerative Joint Disease (DJD) in the
Appendicular Skeleton of Domesticated Cats
Appendicular
Joints Studied
Hips
Hips
All joints
All joints
All joints
All joints
All joints
All joints
Mean Cat
Age (Years)
% of Cats with
DJD of 1 Joint
2.5
2.8
15
Young (75% were o3)
6.5
8.2
11
14
19
6.3
64
30
23
22
—
—
Most Commonly
Affected Joint
Reference
—
—
Elbow
Elbow
Hip
Elbow
Elbow
Hip
Langenbach et al15
Keller et al17
Hardie et al9
Pacchiana et al18
Clarke et al11
Godfrey19
Clarke & Bennett1
Lascelles et al84
For some entries, data cannot be given because of the design or nature of the study (see text for full details). Deﬁnition of OA and DJD varies between
studies.
LASCELLES
Fig 4. Oblique projection of the elbow. There is soft tissue
mineralization, conﬁrmed by macroscopic inspection to be in
the craniomedial joint capsule. It is unknown if such periarticular mineralization is associated with degenerative joint disease.
ing osteochondrodysplasia affects both bone growth and
formation of articular cartilage. Osseous deformities are
most apparent in the distal appendicular skeleton, with
affected joints having the appearance of an ankylosing
polyarthropathy with smoothly marginated periosteal
bone around the carpal and tarsal bones.5,24,25 The beststudied feline form is MPS VI, which causes skeletal
malformation that results in arthropathies.6 MPS VI is a
lysozomal storage disease caused by a deﬁciency of the
lysozomal enzyme N-acetylgalactosamine-4-sulfatase.30
Several case reports and small case series have been published26–32 and the radiographic signs described. In the
appendicular skeleton, coxofemoral subluxation, generalized epiphyseal dysplasia, and DJD occur secondary to
accumulation of abnormal levels of glycosaminoglycans
in cartilage and connective tissue.
Although several authors have suggested that a large
proportion of DJD in cats is primary,11,19 there is currently no supporting evidence. It is very possible that
hitherto unrecognized factors, such as those that play a
role in other species, may be responsible for DJD in cats.
It is also possible that as yet unrecognized factors that do
not play a signiﬁcant role in DJD in other species, such as
systemic inﬂammatory disease, may predispose to, or be
the cause of, DJD in the cat.
Currently documented secondary causes of DJD in
cats are nutritional, HD, and noninfectious polyarthropathies and infectious arthropathies. Hypervitaminosis A
7
in cats occurs when diet consists mainly of liver,33–35 and
results in progressive new bone formation on vertebrae
resulting in ankylosing spondylopathy, and also around
shoulder and elbow joints at ligament and tendon insertions.
HD was described in several cats in the 1970s.36–38 The
dysplastic changes lead to secondary DJD, and the occurrence of degenerative changes in the coxofemoral
joints associated with HD was conﬁrmed by Hayes et al39
who suggested that the prevalence of HD was 1/180th of
that in dogs at the same diagnostic facilities.39 Familial
genetics was suggested as playing a role, because a potential predisposition was observed in pure bred cats, although there were insufﬁcient cases to test this
hypothesis. Medially luxating patellae occurred concurrently with HD and was also suggested as a cause. A
relationship between HD/laxity and coxofemoral joint
DJD was also demonstrated in Langenbach’s study.15 In
a nonrandomly selected, mainly pure-bred group of 78
cats, 15 of 25 cats with HD also had DJD, and the mean
Norberg angle (NA) in cats with DJD was signiﬁcantly
lower than in cats without DJD (84 versus 951), and the
distraction index was signiﬁcantly higher (0.6 versus
0.49). These ﬁndings were similar to those of Koeppel
and Ebner40 who studied NA in relation to DJD in a
random population of domestic shorthair cats.
In Keller’s retrospective evaluation of the incidence of
HD in young cats, 43 of 45 cats with HD had degenerative changes, and all of these had a shallow acetabulum.17 It was noted that the shallow acetabulum is
similar to the situation occasionally observed in humans;
however, acetabular dysplasia does not appear to be a
predictable risk factor for development of DJD in humans.41 No objective measure of acetabular depth was
used; an acetabulum was considered shallow if o50% of
the femoral head was covered.17 Whereas, this could be a
primary structural defect, it is also possible that cats began with normal acetabular depth, but because of hip
joint laxity and subsequent secondary changes, inﬁlling
occurred. Certainly, however, the radiographic appearance of coxofemoral joint DJD appears to be different in
cats than dogs, with overall less bone formation on the
femoral neck and head, and often-prominent new bone
on the cranial effective acetabular rim.17 Histologic studies are needed to determine the role that congenital acetabular dysplasia plays in feline hip DJD. Although
studies that have been performed suggest a relationship
between HD and DJD, these studies have concentrated
on cats with HD.
To further investigate the relationship between HD
and coxofemoral joint DJD, prospective longitudinal
studies are needed where a cohort of young cats are
thoroughly evaluated for hip laxity and conformation,
and then followed over time, with periodic evaluation for
8
FELINE DEGENERATIVE JOINT DISEASE
coxofemoral DJD. In a group of predominantly purebred cats, a weak association was found between medial
patella luxation and HD,42 with a combination of HD
and patella luxation being 3 times more likely than either
condition alone. The weak association may reﬂect the
small number of cats in the study. It was suggested that
patella luxation was congenital because of the young age
of presentation (2 years old) and the mainly bilateral
(71%) nature of the condition. DJD was also observed in
association with patella luxation; however, the relationship between patella luxation and development of DJD of
the stiﬂe is not clear.
Smith et al42 reported that only cats with grade 2 or 3
medial patella luxation had evidence of DJD in the
affected stiﬂe joint. In the only other published report of
patella luxation in cats,43 42 cats were evaluated; 27 cats
(44 stiﬂe joints) had radiographs that were scored according to published criteria for dogs.44 Out of a possible
score of 27, 14 joints had a score of 0; 24 joints, a score of
1–9 (mild OA); 3 joints, a score of 10–18 (moderate OA);
and 3 joints, a score of 19–27 (severe OA). The 3 cats with
severe OA had grade 4 luxation. This data suggest that
increasing severity of patella luxation in cats is more
likely to lead to DJD in that joint. Again, as noted earlier,
the sensitivity of radiographs for detection of DJD in cats
is unknown, and there have been no reported morphologic evaluations of feline joints with, and without, patella luxation.
Although trauma is an often-quoted cause of DJD in
cats,7,45 there is only sparse evidence to support this,1,11,19
and no studies evaluating the occurrence of DJD after
joint trauma (e.g., fracture, dislocation).
Several forms of feline DJD with a suggested immune
mediated basis have been described.46–49 Initially, 5 cases
of polyarthritis48 were described, similar to an earlier case
report47 and the term ‘‘chronic progressive polyarthritis’’
used to describe a deforming polyarthritis of predominately the carpal and tarsal joints that was progressive
over a period of weeks, and associated with pyrexia and
lymphadenopathy. Later, when more cases were evaluated, it appeared that 2 forms existed—a more common
form (17/20 cats), characterized by periosteal new bone
formation and osteoporosis, and a less common form
(3/20) characterized by a deforming, erosive arthritis.49 A
larger series of suspected immune-based polyarthritis with
detailed evaluation, suggested classiﬁcation of feline immune-mediated polyarthritis as: feline rheumatoid arthritis, feline systemic lupus erythematosus, feline periosteal
proliferative polyarthritis, and feline idiopathic polyarthritis.46 Erosive lesions were observed in feline rheumatoid arthritis, and new bone production in feline periosteal
proliferative polyarthritis and to a lesser extent in feline
idiopathic polyarthritis.46 Immune-mediated disease was
considered the underlying cause in all of these cats.
Bacterial arthritis is occasionally seen as a cause of
DJD. Polyarthritis has been associated with Mycoplasma
gateae infection50,51 and monoarthropies with Mycoplasma
felis.52 Recently, bilateral tarsal DJD associated with
cryptococcosis was reported.53
Anecdotally, it is often suggested that obesity causes
DJD in cats. A causal relationship has not been proven,
but the relationship between being overweight and lameness requiring veterinary care has been evaluated. Associations between starting body condition and speciﬁc
diseases that developed, including lameness, was evaluated in 1457 cats studied over a 4.5-year period.54 Risk of
developing lameness requiring veterinary attention was
signiﬁcantly increased for heavy (hazard ratio ¼ 2.9) and
obese (hazard ratio ¼ 4.9) cats. It was suggested that excess bodyweight or a generalized lipid metabolic abnormality might lead to cartilage damage and OA; however,
the cause of lameness and speciﬁcally if it was associated
with DJD was not evaluated. In a retrospective
radiographic study of the prevalence of DJD in cats, no
signiﬁcant association between bodyweight and radiographic signs of DJD was identiﬁed.11
Is Feline DJD Associated with Pain?
Although 90% of the cats evaluated by Hardie et al9
had radiographic evidence of axial and/or appendicular
skeleton DJD, only 4% had mention of arthritis or
problems with mobility noted in the medical records. The
records evaluated were referral hospital records and the
cats were not referred for mobility problems. Godfrey19reported that 1/3 (21/63) of cats with radiographic appendicular joint OA had clinical signs of
mobility impairment, and were radiographed for that
reason (lameness, stiff gait, difﬁculty jumping, hindlimb
weakness, shufﬂing forelimb gait, and inactivity). In another study, 16.7% of the cats with radiographic signs of
DJD were lame; however, it was suggested that lameness
per se may not be the most obvious clinical sign associated with feline DJD.11
In a feline cruciate transection model of OA, ground
reaction forces and limb kinematics recovered to presurgical levels over 1 year, despite progression of radiographic OA.55 Indeed, static differences between the
operated and control side disappeared after 3–4 months,
and dynamic loading differences at the walk disappeared
after 6 months. In a discussion of the model, it was indicated that after 5 years the joints have severe radiographic signs of OA without associated pain.56 In
contrast, several studies have identiﬁed cats with radiographic DJD and mobility impairment1,2,57; NSAID administration signiﬁcantly improved mobility. Two of
these studies were not blinded1,57 and used veterinarian
and owner assessments that have not been validated;
LASCELLES
however, an objective measure of activity was used in
addition to owner assessments in the other study.2
Clearly, in some cats radiographically apparent DJD
is likely associated with pain and results in impaired
mobility.
Recent studies have emphasized that lameness is often
not the presenting complaint—rather, owner-observed
impaired mobility.1,2 If the impact of DJD on the quality
of life of cats is to be evaluated, validated methods to
assess pain and mobility impairment need to be developed. There appears to be a mismatch between radiographic and clinical examination ﬁndings. Clarke and
Bennett1 reported data that suggest 34% of joints assumed to be painful on manipulation during a clinical
examination did not have any signs of radiographic OA.
In another study, there was only moderate overlap between the variables, ‘‘radiographic DJD’’ and ‘‘pain on
manipulation’’; 55 joints had radiographic signs of OA
(as deﬁned radiographically in dogs), but only 18 (33%)
were painful on manipulation.2 Pain is difﬁcult to evaluate in cats but further work is needed to conﬁrm this. Of
the 55 joints assessed as painful, 37 had no radiographic
signs of OA. Six of these had other pathology (periarticular soft tissue mineralization or meniscal calciﬁcation), and it may be that such pathology can be
associated with pain. Histologic studies evaluating this
mismatch (painful joints with no obvious radiographic
ﬁndings) are required to shed further light on whether or
not this is a real phenomenon or simply because of misinterpretation of clinical examination ﬁndings.
In all reports of feline immune-mediated joint disease,
cats are reportedly painful, stiff, and reluctant to be manipulated, suggesting that immune-mediated DJD can be
associated with pain in the cat,46–49 but the degree of
discomfort has not been evaluated further. Of 7 reported
cases of feline lumbosacral disease, 5 cats had clinical
signs of pain, hyperesthesia, or reduced activity associated with lumbosacral DJD.58,59
Treatment Efﬁcacy for Suspected DJD-Associated
Chronic Pain
Currently, there is only evidence for NSAIDs having a
beneﬁcial effect (pain alleviating and mobility enhancing)
in painful feline nonimmune-mediated DJD.1,2,57,60
Treatment of an infectious cause of feline DJD has been
associated with a resolution of pain,51,52 as has treatment
of immune-mediated joint disease with immunosuppressive drugs.46–49 The level of evidence for a pain-alleviating
effect of treatments varies from objective measures in
clinical cases,2 to open-label studies with nonvalidated
subjective assessments in clinical cases,1,57,60 to subjective
reporting on clinical cases.46–49,51,52 Other treatments
may be effective but have not been evaluated. Part of the
9
reason for the lack of evidence-based information about
treatment of feline DJD-associated pain is the lack of
validated outcome measures, and partly because of a lack
of understanding of how to diagnose the disease, and lack
of understanding about its causes.
There is concern about use of NSAIDs in cats, especially on a chronic basis, although meloxicam has recently been approved in the European Union for longterm treatment of feline musculoskeletal pain. This concern is generally centered around the perception that
NSAIDs are metabolized more slowly in cats than dogs.
Most NSAIDs are cleared from the body through hepatic
metabolism (often primarily glucuronidation) and then
biliary and/or renal excretion of the resultant polar metabolites. Given the known propensity for reduced glucuronidation of drugs in cats compared with other
species,61–67 differences in NSAID disposition between
cats and other species might be expected. Aspirin, acetaminophen, and carprofen have relatively prolonged
elimination half-lives in cats compared with dogs, most
likely because of slower drug clearance via glucuronidation. In contrast, similar or even reduced drug elimination
half-lives are observed in cats, compared with dogs, for
drugs cleared by oxidative enzymes, including piroxicam
and meloxicam. There are several exceptions, including
ﬂunixin and ketoprofen, both of which are known undergo glucuronidation in dogs68,69 and yet are not eliminated more slowly in cats. Presence of alternate
metabolic and nonmetabolic pathways for drug elimination may compensate for slowed glucuronidation of
NSAIDs in the cat.
Chronic painful disease demands repeated administration of analgesic drugs, and there is little current information on the pharmacokinetic (PK) and toxic effects
of repeated administration of NSAIDs in cats. In cats
administered ﬂunixin 1 mg/kg orally every 24 hours for 7
days, no drug accumulation occurred.70 In fact, the maximal concentration and the AUC024 were less on day 7
than on day 1, suggesting that the drug was eliminated
more rapidly. Serum thromboxane concentrations were
o75% of baseline up to 7 hours after administering ﬂunixin on day 1, but for only 2 hours on day 7. The alanine
aminotransferase (ALT) increased from 11.4 to 21.3 IU/L,
suggesting that liver toxicity may be a problem with
chronic administration. The only other report evaluating
repeated dosing of a NSAID in cats evaluated piroxicam,
and compared the PK values when piroxicam (0.3 mg/kg
orally every 24 hours) was administered for 10 days either
alone or with cimetidine. Compared with day 1, piroxicam half-life was higher on day 10 (11 versus 14 hours) as
was Cmax, and Tmax was shorter on day 10 in cats administered piroxicam alone. Administration of cimetidine
with prioxicam did not make any clinically signiﬁcant
differences to measured PK variables. Four of 7 cats in
10
FELINE DEGENERATIVE JOINT DISEASE
the piroxicam group and 2 of 7 cats in the piroxicam þ cimetidine group had evidence of gastric erosions
at 10 days. Efﬁcacy of piroxicam or ﬂunixin has not been
evaluated for chronic musculoskeletal pain in the cat.
There have been no reports of total joint replacement
in the cat, and only sporadic reports of joint arthrodesis,24,71with 1 reporting arthrodesis for painful DJD.24 As
noted earlier, arthroscopic removal of osteochondral
fragments from an elbow with DJD, suspected caused by
a fragmented coronoid process, resulted in subjective
resolution of lameness.22 There are also a few reports of
clinical signs of pain associated with lumbosacral DJD
being abolished after surgical decompression.58,59
An often posed question is ‘‘do cats with musculoskeletal pain need to be treated?’’ Their small size and the
fact that they are not generally expected to perform activities or go for walks like dogs has led to suggestions
that they are able to adapt their lifestyles well and ‘‘cope’’
with any discomfort. This question will be better answered once more has been done to evaluate actual and
perceived changes in cats’ activity and quality of life of
cat treated for chronic musculoskeletal pain.
What Outcome Measures are Available to Evaluate
Painful Feline DJD?
Pain associated with joint disease can result in impaired or decreased limb use. Cats have been the subjects
in experimental locomotion studies that have focused on
the organization of muscle reﬂexes during locomotion,
during posturing, equilibrium and body segment movement, and on joint mechanics.56,72–79 Systems most commonly used in dogs to measure kinetic variables (force
plates) cannot be easily used in cats, although miniature
triaxial force plates have been used in the standing cat,77
and force plates have been used to measure limb loading
in standing cats as part of studies evaluating cruciate ligament deﬁcient experimental cats.55,75 Recently, use of
pressure sensing walkway devices have been described for
assessment of acute limb pain in cats after onychectomy80–83 and also for deﬁning normal kinetic variables
in cats.84 The same system was not useful in assessing
pain relief because of the multiple limbs involved in clinical cases with DJD (unpublished data); however, further
work is needed.
Pain from knee and hip joints in humans can often
result in decreased mobility and decreased distance
moved.85 This decreased distance moved appears to be
both total daily distance, and also distance moved in a
single effort. Likewise, in dogs and cats, OA is also assumed to impair mobility and daily distance moved.57,86–88
Evaluation of a small accelerometer found that activity
counts generated by the accelerometer correlated well
with objectively measured activity in cats.89 The same
device was subsequently used in client-owned cats in the
home environment and appeared promising as an objective measure of total distance moved.2 Assuming that
painful DJD results in decreased total distance moved in
cats, then such measures may be a valid means of both
assessing treatments for DJD-associated pain, and also
for evaluating other assessment methods, such as ownerbased assessments; however, there is much to learn about
the data generated by accelerometers. Any movement—
forced or spontaneous—will create ‘‘activity counts,’’ and
disease and treatment may have different effects on activity at different times of the day. External inﬂuences in
the home (e.g., visitors, new pets, other activity) may well
signiﬁcantly affect activity of cats being evaluated.
Subjective assessment of cats with musculoskeletal
pain has been described57,60 but subsequent studies have
highlighted the fact that clinical signs do not generally
include lameness or gait disturbances.1 Instead, it appears
that altered behavior in the home environment may be
the best way to assess musculoskeletal pain—lack of socializing, lack of jumping, decreased height of jumping,
reduced grooming, hiding, and grumpiness1; however,
little is known about what behaviors should be evaluated,
and there are currently no validated owner-based subjective assessment systems for use in cats with chronic
DJD-associated pain. Generation of a valid questionnaire
is a time-consuming and expensive process, consisting of
item generation, readability testing of the instrument, reliability testing of the instrument (test–retest) and ﬁnally
testing the instrument for validity and sensitivity by comparing outcomes from the instrument to objectively measured variables. Indeed, such systems are only beginning
to be developed for dogs despite the substantial knowledge base for DJD in dogs.87,90,91 Despite the difﬁculties
involved, understanding which treatments may be effective in chronic musculoskeletal pain in cats will advance
little until there are validated outcomes measures applicable to clinical cases.
Models of DJD Pain in Cats
Clearly, there is a need for a model of DJD-associated
pain and mobility impairment in the cat. Any model
should be histologically similar to the naturally occurring
disease and have pain as a feature. These requirements
have only fairly recently been identiﬁed as being important in DJD pain research in the basic sciences.92 Further,
it would be ideal if the model of DJD used a clinically
relevant joint. Currently, there is only 1 feline model of
chronic joint OA. In this cruciate transection model,
ground reaction forces and limb kinematics recovered to
near presurgical patterns over the 1-year-period postoperatively, despite progression of radiographic OA.55 It
has been suggested that despite substantial progression of
LASCELLES
signs of OA over a 5-year period, the joints did not seem
to be causing pain.56 Urate crystal induced synovitis has
been studied as an acute model of feline joint pain.93,94
After injection of 20 mg sodium urate crystals into the
stiﬂe joint, signs of lameness occurred within 1 hour,
reaching a maximum after 2–4 hours, lasting for 6–8
hours, and limb use then returned to normal over the
next several days. That sodium urate injection is associated with pain was demonstrated by a decreased lameness
after administration of morphine93 or meloxicam.94 This
model may well reﬂect changes seen in the synovium in
naturally occurring disease, but this has not been evaluated.
Future Directions
Of immediate interest would be information on how
prevalent radiographic DJD is in a randomly selected cat
population that is representative of the larger cat population, and whether radiographic DJD is obviously associated with any particular characteristics, e.g., age, breed,
sex, indoor/outdoor status, etc. Likewise the relationship
between radiographic appearance and morphologic features, particularly histologic characteristics, requires investigation to better understand the mismatch between
radiographic and clinical examination ﬁndings. As this
data is evaluated, hypotheses need to be formulated
about possible causes of DJD in different joints, and
careful observation and collection of general health status
data, in addition to comparisons with other species, will
help in guiding investigations. Determination of the
causes or predisposing factors will help guide treatment,
and in this respect, there is a very real need for validated
subjective and objective assessment systems for the measurement of chronic DJD-associated pain in the cat. Development of a feline model of chronic DJD associated
pain will help speed the development and evaluation of
candidate pain-alleviating compounds and treatments.
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